1. Field of the Invention
The present invention relates to a rolling bearing, and particularly, to a rolling bearing which is suitable for rotational support members of hard disk drives (HDD), video tape recorders, office automation equipment and so forth.
2. Description of the Related Art
As shown in FIG. 4, a rolling bearing 10 consists of an inner ring 11 and an outer ring 12 each having a raceway surface, and a plurality of rolling elements 5 such as balls. Each rolling element 5 is rollably arranged between the raceway surface of the inner ring 11 and the raceway surface of the outer ring 12. Additionally, a retainer 1 rotatably holds each rolling element 5 and ring-shaped sealing members 13 are arranged at each end in the axial direction.
The retainer 1, as shown in FIG. 5, is a ring body having a plurality of ball pockets 2 arranged at equal spacing therebetween, and is resin molding which is molded in one piece. The ball pockets 2 are parts for holding the rolling elements 5 (see FIG. 4). A pair of claws 3 provided at each ball pocket 2 prevents the rolling elements 5 from falling out, and can rotatably hold the elements. Grease resevoirs 4 are arranged at equal spacing between the claws 3 adjacent ball pockets 2. The individual rolling elements 5 are arranged at equal spacing therebetween by the retainer 1, thereby preventing seizure caused by the mutual contact of the rolling elements 5.
Since the retainer 1 does not directly support a bearing load, the retainer may be made of a material having a lower strength than the rolling elements 5, the inner ring 11 and the outer ring 12. However, the retainer 1 is in sliding contact with the rolling elements 5, the inner ring 11 and the outer ring 12. For instance, while the inner ring 11 is rotating and the outer ring 12 is stopped during use, the rolling elements 5 rotate and revolve around the inner ring 11. The retainer 1 is driven by the rolling elements 5 while the ball pockets 2 and the rolling elements 5 are in sliding contact with each other, and the retainer 1 rotates around the inner ring 11 at the same speed as the revolving speed of the rolling elements 5. Thus, the retainer 1 has to resist abrasion and seizure, and is often made of a synthetic resin such as nylon 66 by injection molding.
The retainer 1 molded from such a material can be elastically deformed. Thus, after the resin is injected into a die and solidified during injection molding, a product is released from the die by so-called forced pull-out wherein the claws 3, having an undercut shape in the releasing direction, are widened outwardly, thus simplifying the structure of the die. Moreover, during the assembly of the rolling bearing 10, the tips of the claws 3 of the retainer 1 are pushed outward and the rolling elements 5 are pushed into the ball pockets 2. Thus the rolling elements 5 can be held rollably.
The claws 3 of the retainer 1 are made thin in consideration of the releasing property from the die and the assembling property of the rolling elements 5 described above, which has the following influence on the characteristics of the rolling bearing 10.
A clearance is provided at a required distance between the retainer 1 and the rolling elements 5 or bearing rings of the inner ring 11 and the outer ring 12. However the retainer 1 vibrates despite the clearance being filled and supplied with grease. In addition, noise, the so-called retainer noise, and vibration are generated. Specific causes for the retainer noise are such as:
(1) collision between the retainer 1 and the rolling elements 5 or bearing rings of the inner ring 11 and the outer ring 12,
(2) self-excited vibration due to sliding friction between the rolling elements 5 and the retainer 1,
(3) collision between the retainer 1 and the rolling elements 5 due to grease resistance,
(4) vibration due to waviness of the raceway rings surface of the inner ring 11 and the outer ring 12, and rolling contact surfaces of the rolling elements 5, and
(5) vibration frequency of the shaft portion is close to the resonance frequency of the retainer 1.
In addition, run-out is found in revolution frequencies of the rolling elements 5 due to mutual differences in diameter of the rolling elements 5 and disproportionate arrangement of the rolling elements 5 in a circumferential direction. Accordingly, the vibration fluctuates during the rotation of the rolling bearing 10, and non-repetitive run-out (NRRO) intensifies. Thus, infinitesimal displacement occurs, which results in uneven rotation of HDD and so forth and to deterioration of performance by characteristics such as NRRO. Particularly, when the rolling bearing is used at high rotation (12,000 to 15,000 rpm), a force from the rolling elements 5 works on a thin part of the retainer 1, thus deforming the retainer. In addition, the claws 3 are expanded, increasing the moving area of the rolling elements 5 and thereby intensifying collision noise. The rolling elements 5 are also greatly shifted, which results in the disproportionate arrangement of the rolling elements in the circumferential direction and the deterioration of the NRRO.
Accordingly, it is an object of the present invention to impart strength and rigidity to a retainer to prevent if from deformation by force coming from the rolling elements and sliding friction without deteriorating its releasing property from a die and assembling property of the rolling elements, thus preventing retainer noise and NRRO deterioration of a rolling bearing.
In order to solve the above problems, a rolling bearing according to a first aspect of the invention comprises a resinous retainer having a pair of claws at each of a plurality of ball pockets arranged at equal spacing therebetween so as to prevent rolling elements from falling out, and a separate reinforcing member fixed to the retainer. In other words, since the separate reinforcing member is fixed to the retainer in the present invention, strength and rigidity of the retainer is improved.
Moreover, the reinforcing member may have an annular plate and a plurality of bosses fixed to grease resevoirs of the retainer. According to the present invention, the bosses connect the annular plate to the retainer, and the strength and rigidity of the retainer can be improved due to the rigidity of the annular plate. The grease reservoirs are preferably arranged at an equal spacing therebetween on the circumference of the retainer, so that the strength and rigidity of the retainer can be equally improved over the entire circumference by connecting the bosses to the retainer at the grease reservoirs.
The annular plate may have openings so as not to touch the rolling elements. In this configuration, the annular plate and the rolling elements are by no means in contact with each other even when the retainer is set closer to the annular plate. Thus, a space for setting the reinforcing member can be reduced as much as possible, and the bosses can be shortened as much as possible, thereby preferably improving the rigidity and strength of the retainer.
Furthermore, the grease resevoirs of the retainer can be provided with holes to which the bosses of the reinforcing member are press-fit. In this configuration, the reinforcing member can be fixed to the retainer more simply.